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| Home > Publications database > Keramiken des Monazit-Typs zur Immobilisierung von minoren Actinoiden und Plutonium |
| Book/Dissertation / PhD Thesis | FZJ-2015-05731 |
2015
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-076-0
Please use a persistent id in citations: http://hdl.handle.net/2128/9286
Abstract: The safe disposal of radioactive waste in deep geological formations is a challenging task of present and future generations. Innovative strategies as the conditioning of radionuclides in ceramic matrices can make a contribution here. This work points out monazite-type ceramics as potential waste forms for minor actinides and Pu. Several aspects concerning nuclear disposal as well as fundamental structural information were investigated. Lanthanide phosphate endmembers (LnPO$_{4}$) within the stability field of monazite (Ln = La-Gd) were synthesised within the scope of this work. To extend the knowledge of monazite phases, monoclinic TbPO$_{4}$- and DyPO$_{4}$-phases were prepared and characterised. Tb- and Dy-phosphates are situated in the xenotime stability field close to that of monazite. They can exist as metastable monazite phases. Structural characterisations of long- and short-range order were performed by X-ray diffraction, infrared (IR) and Raman spectroscopy. Structural data could be complemented, enhanced and gaps of knowledge could be filled by the first systematic consideration of the complete Ln-monazite-series (Ln = La-Dy). Furthermore, this work focuses on Sm-monazite phases. Samarium with an atomic number of 62 is located in the middle part of the lanthanides showing the monazite structure. Accordingly, it has a mean cationic radius within the Ln-monazite-series and hence shows a relative high flexibility regarding the incorporation of radionuclides with different radii. Sintering densities of SmPO$_{4}$ ceramics were optimised by varying process parameters like pressure and number of pressing steps. An irregular texture as well as densities of 94% of the theoretical value could be achieved. The resistance of Sm-monazite against ionising radiation were examined. Radiation damages caused by the $\alpha$-decay of radionuclides incorporated in a ceramic matrix were simulated by computer calculations and experimentally by heavy ion bombardment of SmPO$_{4}$. Thin layers of the samples bombarded with Au ions show initiating effects of radiation damages enduring doses of D$_{dpa}$ = 0.02 and 0.06, respectively, whereas a dose of D$_{dpa}$ = 1.65 produced an amorphisation to a great extent in a lamella sample. However, crystalline areas remained due to recrystallisation processes in the material. The flexibility of the Sm-monazite’s crystal structure, necessary for the incorporation of radionuclides, is required for the use of SmPO$_{4}$ ceramics as a suitable waste form. Therefore, Sm was substituted by other lanthanide cations, that served as surrogates for minor actinides such as Np, Am, and Cm or for Pu. Actinides reveal a similar [...]
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